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7 (r+3s) - 2(2r -9s)

Multiply the # outside the parenthesis by each item inside the parenthesis to remove the parentesis and then combine the like terms (r's & s's).

7r + 21s - 4r + 18S
then combine like terms

7r +21s - 4r +18s
7r-4r =21s+18s

3r+39

Does this sound correct.

Yes , but 39s

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